1. Field of the Invention
The invention relates to a novel process for hydrolyzing plant carbohydrates to xylose.
2. Description of the Prior Art
Plant biomass is a promising substrate for ethanol fuel production due to its ready availability and low cost. Most fuel ethanol is currently produced from hexose sugars derived from corn starch or cane syrup utilizing either S. cerevisiae or Z. mobilis. However, these are relatively expensive sources of biomass sugars and have competing value as foods. Moreover, starches and sugars represent only a fraction of the total carbohydrates available from plant material. Most of the available plant biomass is from sources such as residues and by-products from agriculture, gardening, and forestry, including straw, hulls, stalks, pulping wastes, sawdust, wood chips and other cellulosic materials. The principal component of the plant biomass from these sources is found as lignocellulose, making up approximately 90% of the dry weight of most plant material. Lignocellulose typically comprises approximately 30-60% cellulose, by weight, 20-50% hemicellulose, and 10-30% lignin. Cellulose is a β-glucan, a polymer of D-glucose units, while hemicellulose is a complex heteropolymer, the majority of which are predominantly polymers (e.g., xylooligosaccharides) of pentose sugar units such as D-xylose and D-arabinose, as well as smaller amounts of hexoses such as mannose, galactose, and glucose. Thus, hydrolysis of cellulose and hemicellulose releases a mixture of neutral sugars which include glucose, xylose, mannose, galactose, and arabinose. Of these sugars, the amount of xylose is second only to glucose in most plant materials.
Because of its abundance in plant biomass, xylose presents potentially significant economic resource for producing ethanol fuels and other valuable products. Methods of saccharifying lignocellulosic materials include acidic or alkaline pretreatments, followed by enzymatic hydrolysis. The use of enzymatic hydrolysis for as much of the saccharification process as possible is desirable for its mild reaction conditions that consume lower amounts energy and produce lower amounts of toxic waste products.
However, owing to low efficiency and high costs of enzymes, the need persists for improved methods for hydrolyzing plant biomass to produce xylose.